This invention relates to an automatic apparatus for determination of the boron and Li-ion concentrations of the primary cooling water in a pressurized water reactor plant.
Generally, the output of the pressurized water reactor is controlled by adding the boron to the primary cooling water and by changing the concentration thereof. Therefore, the determination of the boron concentration is essential for the operation control of the reactor.
Since the boric acid sample water is a weak acid similar to a non-electrolyte, it has hitherto been proposed that a mannitol or other polyvalent alcohol solution be added with a certain mixing ratio to the boric acid sample water to form a boric acid-mannitol complex, thereby to increase the conductivity for the measurement thereof with an electrode so that the boron concentration (p.p.m.) may be calculated from the mutual relation between the conductivity and the boron concentration.
However, the primary cooling water of a pressurized water reactor contains not only boron of the order of 1,000 ppm but also other cations such as Li-ion of the order of 1 ppm which lead to the erroneous measurement of the conductivity, because LiOH especially is a strong electrolyte.
Therefore, the sample water has hitherto been passed through an ion exchange resin to first remove cations (especially Li-ion), and then the mannitol solution is added for measurement of the conductivity to avoid a detrimental influence of the cation contained in the sample water.
After the ion exchange resin material has been used for the measurement, the deteriorated or contaminated resin must be quickly replaced by fresh resin material. However, on the treatment of the primary cooling water in the atomic power plant, the radioactive matter such as Li is precipitated in or absorbed by the resin material with elevated level of the radioactivity. If the operator directly touches the radioactively contaminated resin, he will likely become exposed to dangerous radioactivity and hence the handling of the waste resin becomes extremely difficult.
In view of the foregoing, a convenient and safe system has now been found for replacing the waste or contaminated ion exchange resin from a fixed container for precipitating or absorbing the radioactive material contained in the sample. The container, at its inlet side, is connected to a flexible tube communicating with a boric acid sample water supply system through a quick connector. The fixed container at its outlet side is connected through a three way valve to a boron concentration measuring system and to a water supply and drain system in which one or more exchangeable containers for storing fresh resin and/or receiving the waste material transferred from the fixed container is releasably arranged in juxtaposition with the fixed container. Said exchangeable container at its opposite ends is provided with quick connecting terminals, one of which is releasably connected to a mating quick connector terminal secured to the end of the flexible tube, whereas the other terminal is connected to a mating quick connector terminal of the tube connected to the three way valve, which selectively communicates with the water supply or drain system.
The fixed container containing the deteriorated or waste resin is connected at its inlet side to one end of the flexible tube which, at its opposite end, is in turn connected to the exchangeable container for recovering the waste resin so that the waste resin is transferred from the fixed container to the exchangeable container under water pressure by the operation of the three way valve. Then, the exchangeable container for recovering the waste resin is replaced by another exchangeable container containing therein fresh active resin which is subsequently transferred into the field container with water supplied by the operation of the three way valve. Finally, the flexible tube connected to the inlet side of the fixed container is returned to its original position to achieve a convenient and quick replacement of the waste or contaminated resin by the fresh and active resin.
In this system, two separate exchangeable containers are arranged in connected relation to the fixed container. The first exchangeable container is filled with fresh resin material and a second container is left empty. In this arrangement, the contaminated ion exchange resin material in the fixed container is transferred into the second or vacant container and the fresh resin contained in the first container is then moved into the fixed container. When the resin material in the fixed container is contaminated, it is fed back to the first container. Thereafter, the first and second exchangeable containers, each containing contaminated resin materials, are replaced by another first container filled with resin material and a second container left empty for the next replacement operation.
The exchangeable containers may be made of a transparent material such as transparent synthetic resin with a desired scale indication provided on the surface of the container for indicating the quantity of the resin to be received, so that the replacement of the proper amount of resin may be conveniently observed.
As described hereinbefore, the determination of the boron concentration may be carried out without errors by use of the ion exchange resin. In employing an ion exchange resin, however, the determination result is obtained following a time lag during which the adsorption of Li-ion increases, resulting in the accumulation of the radioactive substance in the resin material. As the result, the radioactivity may not be neglected and the treatment of the waste resin becomes extremely difficult. In the measurement of the conductivity of the mixture of the boric acid sample water and the mannitol solution, but in the absence of ion exchange resin in order to avoid the disadvantage as hereinbefore described, it has been found that the resulting determinations of the boron concentration varies in relation to the Li-ion content in the sample water.
In view of the foregoing fact, it has been found that the ideal automatic determination of boron and Li-ion concentrations may be carried out without any conventional disadvantage when the first and the second electrodes for measuring conductivity are arranged, respectively, before and following the mixing of the boric acid sample water with the mannitol solution. The Li-ion concentration is determined by measuring the conductivity of the sample water before the mixing with the mannitol. The boron concentration including errors is determined by measuring the conductivity of the sample water after the mixing with the mannitol. The two measurements thus obtained are put into the calculating circuit to carry out the calculation for correction depending on the variation of the conductivity in the presence of Li-ion, and the resulting determinations are indicated by an indicator.
Thus, after the measurement k.sub.1 (.mu. /cm) with the first electrode before the mixing of the sample water with the mannitol solution and the measurement k.sub.2 (.mu. /cm) with the second electrode after the mixing has been effected, the boron concentration C.sub.B (p.p.m.) may be calculated using the known equation with the afore-mentioned k.sub.2. For example, when the mixing ratio of the sample water with the mannitol solution (10 W/O) is 1:1, the equation is as follows: EQU .sqroot.C.sub.B ={6.25.times.10.sup.-2 (log k.sub.2 -1.95).sup.2 +0.1968} k.sub.2 ( 1)
The boron concentration C.sub.B thus obtained, however, includes an error due to the Li-ion content because the conductivity has been measured in the presence of the Li-ion. Therefore, the boron concentration C.sub.B (p.p.m.) should be corrected to eliminate the effect of the Li-ion concentration C.sub.Li (p.p.m.).
Accordingly, the relationship between the Li-ion concentration C.sub.Li (p.p.m.) and the measurement of the conductivity k.sub.i (.mu. /cm) is determined with the parameter of the boron concentration C.sub.B (p.p.m.) to obtain the characteristic lines as shown in FIG. 1. From the characteristic lines the Li-ion concentrations C.sub.Li (p.p.m.) may be calculated on the basis of the measurement k.sub.1 (.mu. /cm), according to the following three equations:
(1) In case of the boron concentration C.sub.B being 1,500 to 3,000 p.p.m. EQU C.sub.Li (p.p.m.)=0.099 k.sub.1 -0.43 (2)
(2) In case of the boron concentration C.sub.B being 500 l to 1,500 p.p.m. EQU C.sub.Li (p.p.m.)=0.093 k.sub.1 -0.28 (3)
(3) In case of the boron concentration C.sub.B being 250 to 500 p.p.m.. EQU C.sub.Li (p.p.m.)=0.093 k.sub.1 -0.21 (4)
Thus, the Li-ion concentration may be obtained.
On the other hand, the relationship between the Li-ion concentration C.sub.Li (p.p.m.) and the measurement k.sub.2 (.mu. /cm) is determined with the parameter of the boron concentration C.sub.B (p.p.m.) to obtain the characteristic lines as shown in FIG. 2. From these characteristic lines, the boron concentration C.sub.B (p.p.m.) may be correctly calculated on the basis of Li-ion concentration C.sub.Li (p.p.m.) and the measurement k.sub.2 (.mu. /cm) according to the following equations:
(1) In case of the boron concentration C.sub.B being 500 to 3000 p.p.m. before correction; ##EQU1##
(2) In case of the boron concentration C.sub.B being 250 to 500 p.p.m. before correction; ##EQU2##
Moreover, we have devised a new apparatus for determination of the boron concentration through measurement of the conductivity of the mixture of the boric acid sample water with the mannitol solution. In this apparatus, a heat sensitive element of metallic filament, which is sharply sensitive to a liquid temperature at a conductivity measuring position, is dipped in a conductivity measuring tank to detect the change of the liquid temperature by means of variation of an electric resistance; this enables correction of errors in measurements of the conductivities on account of changes of the temperature. The conductivity of the sample water consisting of the boric acid-mannitol complex has a negative temperature coefficient of 0.36% per 1.degree. C. in the range of temperature of from 20.degree. C. to 40.degree. C., so that use of a metallic filament having a positive temperature coefficient, which is connected to a temperature correction circuit of the conductivity measuring circuit results in the convenient measurement of the conductivity with the corrected temperatures.